1. Field of the Invention
The present invention relates to a variable shaped electron beam lithography system for drawing a figure pattern including an oblique line with an arbitrary angle by forming a single electron beam shot in the same shape as the figure pattern, and a method for manufacturing a substrate.
2. Description of the Related Art
In a photo mask electron beam lithography system including an electron optical system having a 50 kV electron gun, a raster scan system and a variable shaped beam system (hereinafter, called “VSB system”) have been developed, and at the present day, both of them are put into practical use. The raster scan system is, as shown in FIG. 1A, a system which scans a resist layer of a photographic dry plate (blank) by moving the position of a spot of beam irradiation 31 and by projecting electron beam 30 at a position of target drawing pattern 29. On the one hand, the VSB system is, as shown in FIG. 1B, a system which divides target drawing pattern 29 into a plurality of rectangular figures, forms electron beam shot 32 into an electron beam shape coincident with the divided rectangular figures for each of them, and draws patterns on a dry plate or a semiconductor wafer.
The raster scan system has higher drawing accuracy, but lower throughput because of a large number of shots. Therefore, in the field for manufacturing a critical photo-mask, the VSB system is primarily adopted because the VSB system is expected to draw a fine pattern of several hundred μm accurately at a high speed.
A lithography system of the VSB system, as shown in FIG. 2, forms an electron beam emitted from electron gun 1 into rectangular beam 7 through two apertures 101, 102. Then, the formed rectangular beam 7 is reduced by reducing lens system 6, and the deflection angle of the beam is changed by deflector 9 of object lens system 8 to converge and subject to a drawn target substrate 10.
Specifically, first aperture 101 and second aperture 102 for forming a beam are fixed as shown in FIG. 3, and they have a square opening portion in a plate to shield against an electron beam. Therefore, an electron beam which passed through opening portion 101a of first aperture 101 is formed into the same, square shape as opening portion 101a (FIG. 4 (a)). Then, the electron beam is shifted by deflector 5 of forming lens system 4 relative to XY rectangular coordinates of second aperture 102 in the X-axis direction and/or in the Y-axis direction, generating rectangular beam shape 11 formed by a common opening portion between two aperture 101, 102 (FIG. 3, FIG. 4 (b)). That is, by allowing only a part of the electron beam which passed through first aperture 101 to pass through opening portion 102a of second aperture 102, a desired, rectangular beam 7 is formed. Subsequently, rectangular beam 7 is reduced by reducing lens system 6 to project a desired, rectangular beam shot 12 onto the drawn target substrate 10 (FIG. 3, FIG. 4 (c)).
Nowadays, as an LSI pattern is made finer in higher integration, complexity in an LSI pattern shape drawn on a photo-mask is increased, and also the number of LSI patterns tends to be increased exponentially, as the process generation goes forward. This means that, in a process for directly drawing an LSI pattern on a dry plate or a semiconductor wafer, patterns to be drawn by a lithography system are enlarged, or the number of drawing figures divided into a rectangle by the VSB system is increased. This tendency may be a factor for largely lowering productivity, because the time period required to draw is approximately linearly increased corresponding to an increase in the number of figures.
On the one hand, in drawing a trapezoidal FIG. 13 in which both of the two opposite sides have an oblique line with an arbitrary angle, as shown in FIG. 5 (a), a beam formation method by the VSB lithography system shown in FIG. 2 cannot form an electron beam shot that has an oblique line relative to the rectangular coordinate axis of the target that is to be, drawn (hereinafter, called “drawing rectangular coordinate system”). Therefore, as shown in FIG. 5 (b), the trapezoidal figure is divided into a rectangular figure and a triangular figure, further the triangular figure is finely divided into a plurality of elongated rectangular figures, and single electron beam 14 is formed into a rectangular shape coincident with each of the divided figures, and converged and subjected, respectively. In addition, the lithography system (from NuFlare Technology, Inc., EBM series) normally equipped with the second aperture having an opening side at 45° angle can form a beam shot into a triangle having an oblique side at 45° angle, but cannot be applied, when the triangle has an oblique side at an arbitrary angle. Of course, if an aperture for drawing obliquely is provided, for now, it may be addressed, but an oblique side with any arbitrary angle may not be covered, then it cannot be an actual solution. Further, in the case of FIG. 15 obtained by rotating trapezoidal FIG. 13 shown in FIG. 5 (a) around the center of the figure by an arbitrary angle, as shown in FIG. 6 (a), all four oblique side portions have to be approximated by a plurality of elongated rectangular figures 16 parallel or vertical relative to the XY drawing rectangular coordinate system. Therefore, the total number of divided drawing figures of the figure shown in FIG. 6 (b) is largely increased compared to that of the figure shown in FIG. 5 (b).
In current design of LSI pattern, the mainstream is a system called “Manhattan System” in which a pattern is arranged along an X-axis or a Y-axis direction in the XY drawing rectangular coordinate system. While there have been significant advances in the wiring design of LSI patterns, an element arrangement in a direction that has an arbitrary angle is expected to be a useful means to allow a design region to be used effectively, but this arrangement is not permitted in the current Manhattan System. However, in addition to drawing a photo-mask having LSI design involving such oblique arrangement, in the case of forming a pattern of MEMS (micro Electro Mechanical Systems) or a pattern of a nanoimprinting mold for an optical element, a complex pattern using many oblique sides with an arbitrary angle has to be drawn. As the result, in a drawing process using the current VSB lithography system, the number of the divided drawing figures becomes enormous. Therefore, to improve productivity in this process, the largest, technical challenge is to reduce the number of the divided figures in order to shorten the drawing time.
Then, as for a method for forming an oblique pattern, there are technologies disclosed in Japanese Patent Laid-Open No. 61-255022 and No. 9-82630. In Japanese Patent Laid-Open No. 61-255022, there is disclosed a technology that, by rotating a first aperture and a second aperture shown in FIGS. 13 and 14 in synchronization with each other, a shape of a beam shot is formed into a rectangular pattern having two oblique sides opposite to each other. However, in this drawing method, the other two opposite sides except the opposite, oblique side portions do not become parallel or vertical to the XY drawing rectangular coordinate system. Therefore, there arises a problem of lack of versatility, because it is difficult to connect with rectangular shaped electron beam shot having four sides along the X/Y-axis direction in the XY drawing rectangular coordinate system.
Further, in Japanese Patent Laid-Open No. 9-82630, disclosed is a technology that, in a conventional VSB lithography system having the first and second fixed aperture as shown in FIGS. 2 and 3, a third rotatable aperture having a slit is provided. In this lithography system, in order to conform to a drawing figure pattern including two opposite, oblique sides parallel to each other that are inclined at an arbitrary angle, a rectangular beam formed by the first and second aperture is formed by the slit of the third aperture rotated up to an angle made between the parallel, oblique sides of the target drawing pattern, thereby the oblique side portions are formed. Two opposite sides, except the oblique side portions, are formed horizontally or vertically relative to the XY drawing rectangular coordinate system, by both the first and second aperture. In such a drawing system, a beam shape formed by the third aperture becomes a similar figure to a drawing figure, and the reduction rate in projecting onto a wafer etc. is represented by the ratio of the distance between two oblique sides of a target drawing figure, to the slit width (fixed value) of the third aperture. Therefore, the reduction rate of the formed beam has to be changed, every time a size of the divided figures to be drawn becomes different, and a settling time required for calibration for each reduction rate adjustment is accompanied. Further, when the target drawing figure is in a trapezoidal shape in which opposite oblique sides have an arbitrary angle and are not parallel to each other (FIG. 5 (b), FIG. 6 (b)), the number of divided figures involved in drawing a figure pattern is increased.
The total required drawing time of the VSB system is approximately represented as the product obtained by multiplying the sum of the settling time necessary for a system to deflect a beam for each drawing and the beam emission time in drawing figures (in exposing resist) by the total number of figures to be drawn. Therefore, the larger the total number of drawing figures is, the more the total drawing time is increased.
Further, in the conventional VSB lithography system which divides a drawing figure pattern having opposite, oblique line portions that are inclined at an arbitrary angle into a rectangular figure, and which converges and emits a formed beam for each rectangular figure, the total drawing time is prolonged linearly due to an increase in the total number of divided figures. Therefore, compared to a drawing figure pattern having a completely rectangular shape the side of which are each parallel or vertical relative to the X-axis or the Y-axis direction in the XY drawing rectangular coordinate system, in a drawing figure such as a parallelogram, a trapezoid, and a rotated trapezoid formed by rotating the trapezoid around the center of the figure, the number of rectangular figures approximating oblique side portions is increased, and the total drawing time is prolonged accordingly. To shorten the total drawing time, setting a size of a divided rectangular figure to be coarse may be also effective, but on the other hand, approximate accuracy in oblique side portions is degraded, so that it cannot be a fundamental solution.